Synthesis of 1,2,4-Triazolines: Base-Catalyzed Hydrazination/Cyclization Cascade of α-Isocyano Esters and Amides

A convenient, efficient synthesis of 1,2,4-triazolines from alpha-isocyano esters/amides and azodicarboxylates is presented. The developed reaction cascade is based on a base-catalyzed hydrazination-type reaction followed by a subsequent cyclization providing the triazolines in good to excellent yields (75-99%). Phosphine-catalyzed and preliminary asymmetric phase-transfer catalysis approaches have also been investigated.